1. Field of the Invention
The present invention relates to a sheet processing apparatus and an image forming apparatus. More particularly, the present invention relates to a sheet processing apparatus which cuts an open end portion of a sheet bundle formed by bundling and folding sheets and to an image forming apparatus including the sheet processing apparatus.
2. Description of the Related Art
Some conventional image forming apparatuses such as copying machines and laser printers include sheet processing apparatuses. The sheet processing apparatus performs saddle stitch bookbinding by accepting sheets to be discharged and folding in the middle of the sheets or by accepting sheets, performing a binding process in a substantially middle portion of the sheets, and then folding in half at center of the sheets after images are formed on the sheets.
Conventionally, when a sheet bundle is folded and bound to form a saddle-stitched book (hereinafter called a booklet), an edge serving as an end (open end) on a side opposite to a binding portion of the booklet has been known to be shaped in a triangle with a pointed center in a thickness direction of the booklet. This triangle is unique to a booklet formed by the saddle stitch bookbinding, whereas a booklet formed by side stitch bookbinding, case work bookbinding, or tape bookbinding has a rectangular edge.
When pages of the booklet having such a triangular edge are turned, a next page protrudes from a current page among pages from a front cover to a vertex in a center of the booklet, so that the next page can be picked up with fingers and turned. Among pages from the vertex to a back cover of the booklet, however, a next page is retracted from a current page, and thus the next page cannot be picked up with fingers, causing difficulty in turning the page. On the other hand, when an edge has a rectangular shape, pages can be stably turned without differences in page turning.
Consequently, there are cases where an edge portion of a booklet is cut (sheared) by a cutting process to eliminate the triangular edge unique to the saddle stitch bookbinding. Cutting apparatuses (trimmers) for such a cutting process have been commonly known in the art. For example, Japanese Patent Laid-Open No. 2008-238394 discusses a cutting apparatus that includes a movable blade (upper blade) capable of moving up and down and a fixed blade (lower blade) fixed in a position below the movable blade such that an edge portion of a booklet is nipped between the movable blade and the fixed blade by moving down the movable blade and is cut. Accordingly, the cutting of the edge portion of the booklet can change the edge shape from triangle to rectangle, thereby enhancing the appearance of the booklet as a product and proving stability in page turning.
In such a conventional sheet processing apparatus, when the edge portion of the booklet is nipped between the movable blade having moved down and the fixed blade and is cut, waste generated by cutting the edge portion (hereinafter called cutting waste) is pushed down along a side surface of the fixed blade in a state of being in contact with the movable blade. Subsequently, the cutting waste is dropped into a waste box arranged below the fixed blade.
However, for example, when a booklet includes sheets output from an image forming apparatus that forms images using electrophotography such as static electricity, cutting waste scrap may be adhered to a movable blade due to charged sheets. When such the cutting waste is adhered to the movable blade, the cutting waste is moved up with an upward movement of the movable blade without being dropped into a waste box, causing the cutting waste scrap to adhere to and remain on an upper surface of the fixed blade.
Since the upper surface of the fixed blade serves as a conveying surface for conveying sheets, the cutting waste adhered to the upper surface of the fixed blade is conveyed to a downstream side with the following sheet. Consequently, there have been cases where the cutting apparatus stops for emergency when such conveyed cutting waste is detected by a sensor which detects a sheet. Moreover, the cutting waste conveyed with the sheets is stacked and held with the booklet, causing the possibility of deterioration in booklet quality.
The present invention provides a sheet processing apparatus and an image forming apparatus capable of reducing occurrences of adhesion of cutting waste to a fixed blade.